My main
scientific interests focus on biotic
interactions among
organisms. I explore how animals and plants interact with each other
and among themselves. A major goal is to improve our understanding of
the functioning of biological communities, by identifying both the proximal
mechanisms and the underlying selective forces that shape complex
relationships such as mutualism and competition. My works also fit into efforts to better integrate biotic interactions into studies of major ecological changes such as biological invasions.

To date, I have
focused on different kinds of interactions that insects have both among
them and with various organisms including plants or fungi. Using
approaches of behavioural, nutritional or chemical ecology,
I combine field and laboratory experiments to exlpore the
complex, sometimes indirect ways through which these organisms
interact.

As
a research assistant in the ECC
team of the LEHNA, I investigated the importance of both
inter- and intra-specific interactions in conservation issues.

Some
argue that species interactions must be an integral part of
conservation efforts. This is
particularly obvious when a threatened species maintain close
associations with other
organisms. Such is the case of some Lycaenid butterflies whose complete
life cycle requires
specific plants and ants. I took part in a study characterizing the
relationships among the abundances of the three interacting species in
grasslands of the Rhône-Alpes french region. This work
will provide both methodological recommendations for conservation
managers and new insights in the community context of the
plant-butterfly-ant interactions.

Intra-specific interactions, on the other hand, are more
commonly
taken into account in conservation strategies. In some systems,
however, their detailed study is still crucially needed to improve our
understanding of challenging ecological problems. I undertook such an
approach by conducting experiments to unravel the social organization
of the invasive ant Lasius
neglectus and, ultimately, uncover its invasion history at
a regional scale in the Rhône valley.

2008-2011:
Impact of an invasive wasp on
native ant
communities

(Post-doc - Victoria
University of Wellington,
New Zealand)

The common wasp, Vespula
vulgaris
was accidentally introduced in New Zealand in the late 1970's, and
quickly invaded the whole country. Beech forests are particularly
favorable to the species: abundant scale insects live there, and
produce a large amount of honeydew. This sugar-rich resource is heavily
used by wasps, so that their population density in this habitat is now
one of the highest in the world. As a predator and competitor, V. vulgaris can negatively affect a wide range of native organisms.

Working in the team led by Phil Lester at the CBRE, my
aim was to assess the impacts of invasive wasps on native ant
communities. I examined how ants and wasps interact in the field,
wether they interact directly (when foraging for the same prey) or
indirectly (when honeydew collection by wasps reduce the amount of this
resource for other consumers like ants). I also studied how ants
respond, both individually and collectively, to variations in
macronutrient availability.

This work showed that behavioural plasticity can play an important role
not only in the ecological success of invasive species, but also in the
ability of native species to co-exist with invaders. It also highlights
the needs for more studies linking diet and behaviour, because they can
shed light on the mechanisms behind biological invasions and food
competition in general.

The
evolutionary stability of
mutualisms, or mutually beneficial interactions between species, raises
a
lot of questions. In theory, shifts to unidirectional exploitation are
often
possible as former mutualists evolve towards parasitism or because
external
non-mutualist organisms interfere with established associations.
Paradoxically, mutualisms are everywhere. How
can they
persist in the face of these destabilizing pressures?
I explored this
question in the Guianian myrmecophyte Hirtella
physophora, a shrub bearing leaf pouches that lives
in pristine
rainforests, and
its almost
exclusive inhabitant, the ant Allomerus decemarticulatus.
First, I
examined all the effects that the partners have on each other. Ants
represent an optimal, indirect defence against herbivores,
mainly as a
by-product of their foraging activity. Plants provide
shelter
and nectar, as well as conditions favoring the use of an exclusive
territory. I argue that the global functioning of this mutualism
corresponds to
the concept of pseudoreciprocity, a situation limiting the
possibilities of conflict
between partners. Besides, I
studied the encounter of the two partners to determine what prevents
the
presence of
intruders. I experimentally tested the role interspecific competition,
selective
filters and host recognition by the queens could have. The last
mechanism,
rarely demonstrated, proved to be prominent and could contribute to the
structuring of a compartmentalized community that favors the
perpetuation of
very specific associations.

Native
to the
Neotropics,
the little fire ant Wasmannia
auropunctata
is one
of the most
problematic invasive ants known, with accompanying ecological and
economical
consequences in the numerous areas where it has been introduced.
One of the
aims of our group was to study the ecology of this ant species in its
native
range, in French
Guiana.
My
contribution to this project concerned the
populations found in human-disturbed areas, such as forest
fragments or
roadsides.
I collected extensive demographic data that
confirmed the dominant status of these native populations. I also
evaluated the
possible
mechanisms behind a surprising coexistence between such dominant
populations
and Cyphomyrmex
fungus-growing
ants,
by using both behavioural and chemical approaches.Grangier
J. 2004.
Les populations envahissantes de la fourmiWasmannia
auropunctata
(Roger) dans sa zone d'origine: caractérisation, comparaison
avec une zone d'introduction, et interactions avec l'entomofaune.
Mémoire de DEA, Université de Toulouse,29pp.